1. Field of the Invention
The present invention relates to a method for manufacturing a liquid crystal device which can be readily scaled up to give a large area. The liquid crystal device according to the present invention is useful as a screen for shielding visual field of windows and show windows, as a light-control curtain, and as a liquid crystal display which displays and electrically converts characters, figures, symbols, and the like.
2. Description of the Prior Art
Liquid crystal display devices heretofore used widely in practice include those using nematic liquid crystals, i.e., the TN (twisted nematic) mode or the STN (super-twisted nematic) mode liquid crystals. There has also been proposed recently a liquid crystal electrooptical device using a ferroelectric liquid crystal. However, it is requisite for the devices mentioned hereinbefore to use a polarizer sheet and to impart a regular orientation to the molecules along one direction. On the other hand, there is also known a dispersion type liquid crystal device which realizes high contrast without using any polarizer sheets nor applying such an orientation treatment to the molecules. This dispersion type liquid crystal device comprises a transparent solid polymer having dispersed therein nematic, cholesteric, or smectic liquid crystals in granules or in sponges. The method for fabricating such a liquid crystal device comprises dispersing liquid crystals in a polymer by encapsulating the liquid crystal, and then applying the resulting polymer as a thin film on a substrate or a film. The substances proposed to use in the encapsulation include gelatin, gum arabic, polyvinyl alcohol, and the like.
According to the encapsulating technique set forth above, the liquid crystal molecules having encapsulated in polyvinyl alcohol arrange themselves along the electric field when an electric field is applied, provided that the molecules have a positive dielectric anisotropy in the thin film. In such a case, the thin film turns transparent if the refractive index of the liquid crystal is equal to that of the polymer. When no electric field is applied, the liquid crystal molecules are in random orientation. Thus, the thin film turns opaque since the light cannot be transmitted due to scattering. In addition to the one exemplified above, some more liquid crystal devices comprising a thin film or a film of a polymer having dispersed therein encapsulated liquid crystals are also known. For example, there is known a liquid crystal display device comprising an epoxy resin matrix having dispersed therein liquid crystal materials, a liquid crystal display device which utilizes phase separation between a liquid crystal and a photocurable substance, and a liquid crystal display device which comprises a three-dimensional polymer structure being impregnated with a liquid crystal. Those liquid crystal electrooptical devices described above are collectively referred to hereinafter as dispersion type liquid crystal devices.
To realize a practically feasible large-scale liquid crystal electrooptical device as mentioned earlier, it is particularly required to develop an economical and a simplified technique for fabricating large devices.
In scaling up the liquid crystal device, several problems should be overcome. Since the transparent solid substance to be used in the dispersion type liquid crystals are highly viscous, the commonly used technique of liquid crystal injection does not apply. Accordingly, the liquid crystal should be once fabricated into a thin film on one side of the substrate by methods such as coating and casting, and then it should be fixed by superposing the other substrate on the thin film of the liquid crystal.
Furthermore, it is required in a large-area display that the spacers are uniformly distributed between a pair of substrates to maintain a constant distance between the substrates. However, in the dispersion-type liquid crystals, the fabrication process inevitably involves a method such as coating and casting, and, such a process causes segregation or partial aggregation of the spacers to hinder uniform dispersion thereof. Thus, the liquid crystal electrooptical devices realized heretofore suffered uneven spacing between the substrates.